Process for improving motor octane of olefinic naphthas



y 6, 1969 J. ENG ETAL' 3,442,792

PROCESS FOR IMPROVING MOTOR OC'IANE OF OLEFINIC NAPHTHAS Filed Aug; 17, 1966 JACKSON ENG JOHN L. T/EDJE W Mw PATENT ATTORNEY United States Patent 11.5. CI. 208-62 8 Claims ABSTRACT OF THE DISCLOSURE A process for improving the sensitivity of olefinic naptha by integrating a hydrofining stage at the end of a hydroforming train.

This invention relates to improving the octane number of olefinic naphthas and, more particularly, relates to integrating a hydrofining slep at the end of a hydroforming operation or at the end of a series of hydroforming steps for treating olefinic naphthas along with the hydroformate.

The problem of lowering gasoline sensitivity is becoming increasingly important. The process of the present invention is especially useful in hydroforming systems having some spare capacity and the last hydroformer reactor can be eliminated and a hydrofining reactor substituted for it as the last reactor in the series. Olefinic naphthas have high research octane number, but unfortunately they also have low motor octane numbers (or high sensitivities-difference between research and motor octane numbers) and poor lead response.

A separate hydrofining unit for partially saturating the olefins is an effective unit but is expensive as a separate unit. Because of the highly exothermic reaction, the catalyst must be arranged in several beds with cooling between the beds as by injecting cold hydrogen between the beds as a quench to control the temperature rise.

Where a hydroforming unit is not being used to full capacity, various proposals to improve gasoline sensitivity have been made to utilize the spare capacity in the hydroforming unit. For the cases considered, additional investments were required and sensitivity improvements were not sufficient to meet target levels. In order to process catalytically cracked naptha in the Powerformer, hydrofining severity had to be increased to reduce nitrogen content of the naphtha to an acceptable level. Polymer gasoline could be processed in the Powerformer but yield losses were excessive at normal or conventional Powerforming conditions.

The present invention provides a method for using available Powerforming capacity to produce the desired sensitivity levels at significantly lower cost. With the present invention, the final Powerformer reactor is used as a hydrofiner reactor to achieve the desired partial saturation of olefinic naphthas. In the case where the Powerformer is running well below capacity, the reactors are only partially filled with platinum catalyst. By removing the Powerforming catalyst from the last or number 4 reactor and bloading it into the first three Powerforming reactors, the number 4 reactor can be released for hydrofining.

Olefinic naphtha is mixed with the Powerformate from the third 'Powerforming reactor and the resulting mixture is hydrofined to partially saturate the olefins. The desired degree of saturation will depend on the type of olefinic naphtha, but will generally be in the 30 to 60% range.

By integrating the hydrofiner at the end of the Powerformer, certain advantages are obtained which are not possible with a separate hydrofiner. Investment cost can be reduced significantly because some of the equipment on the Powerformer can also be used for hydrofining. The olefinic naptha or naphthas are added to the Powerformate leaving the last Powerforming reactor and the combined reformate-olefinic naphtha stream is hydrofined over a hydrofining catalyst in a hydrofining reactor to the desired saturation levels.

The feed to the hydroformer or Powerformer may be a virgin naphtha having a boiling range of approximately 160 to 400 F. The naphtha feed is preferably high in naphthenes say up to about 50 vol. percent naphthenes. Also the naphtha feed is preferably desulfurized and denitrogenized before being hydrofor'med. The feed is heated and the resulting vapors contact the catalyst .at an elevated temperature and pressure in the presence of hydrogen.

The hydroforming process itself produces substantial amounts of hydrogen and in actuality the quantity produced is more than sufficient to repress deactivation of the catalyst by carbon formation. Thus, excess hydrogen is available for other needs such as saturation of olefins.

The reactions involved in hydroforming are: (1) dehydrogenation of naphthenes to the corresponding aromatic as where methylcyclohexane is dehydrogenated to form toluene; (2) isomerization of paraffins to form branched chain parafiins or isomerization of ring compounds, such as ethylcyclopentane to form methylcyclohexane, which latter compound is then dehydrogenated to form toluene, (3) dehydrocyclization of paratfins to aromatics such as n-heptane to form toluene, and (4) hydrocracking of the higher boiling constituents of the feed to form lower boiling constituents.

Hydroforming processes may be divided into two general classes, namely, the semi-regenerative and the cyclic. In the latter case, it is possible to use a separate reactor which is, itself, regenerable and may be substituted for any of the other reactors in the circuit while they are being regenerated. This would be obvious to one skilled in the art and, therefore, need not be further described .at this time.

The catalyst is a conventional hydroforming catalyst such as platinum or palladium on a halogen treated alumina. Other hydroforming catalysts such as rhenium on alumina, chromia on alumina may be used and other supports such as silica-alumina may be used.

The polymer gasoline is produced by a conventional process using a mixture of propylenes and butylenes at a temperature of between 50 F. and 300 F., a pressure of between 200 p.s.i.g. and 1000 p.s.i.g. with catalysts such as phosphoric acid, sulfuric acid or aluminum chloride. In polymerization, light olefinic molecules are combined to form heavier olefinic molecules boiling within the gasoline boiling range. While these polymerized components possess high octane ratings, they have a high sensitivity and this results in unsatisfactory fuel performance in the more recently developed engines.

Catalytically cracked naphtha is produced by conventional catalytic cracking of gas oils.

With the present process, the leaded motor octane number of the polymer gasoline and/or catalytically cracked naphtha or gasoline and mixtures thereof is substantially increased and the leaded reserach octane number is decreased only slightly so that there is a net reduction in sensitivity.

In the drawing, the figure diagrammatically represents one form of apparatus adapted to carry out the process of the present invention.

Referring now to the drawing, the reference character 10 designates a line for introducing a naphtha feed boiling between about F. and 450 F. to a series of hydroforming reactors presently to be described. Hydrogencontaining gas or recycle gas is mixed with the naphtha from line 12 and the mixture is passed through furnace or heater 16 where it is heated to a temperature between about 850 F. and 975 F., and a pressure of between 100 p.s.i.g. and 500 p.s.i.g.

The heated mixture of naphtha and hydrogen-containing gas is preferably passed into the top of the first hydroforming reactor 18 containing a sufiicient amount of catalyst to provide for a space velocity of 4 to w./ hr./w. (weight of oil per hour per weight of catalyst). Three hydroforming reactors are usually provided but more may be used if desired.

Catalysts that may be used for hydroforming the feed are those containing 0.0l1.0 weight percent platinum or 0.1-2.0 weight percent palladium dispersed upon a highly pure alumina support such as is obtained from aluminum alcoholate, as per US. Patent 2,636,865 or from an alumina hydrosol prepared by hydrolyzing aluminum metal with dilute acetic acid in the presence of a very small catalytic amount of mercury. A suitable catalyst comprises about 0.2-0.8 weight percent platinum widely dispersed upon alumina in the eta or gamma phase derived from a suitable aluminum alcoholate and having a surface area of about 50300 square meters/gram.

Due to the endothermic reaction in the first reactor 18, there is a reduction in temperature of the naphtha being hydroformed. The temperature of the hydroformate in line 22 is between about 800 F. and 875 F. The Powerformed or hydroformed products leave the bottom of reactor 18 through line 22, are passed through second heater or furnace 24 and introduced into the top of the second hydroforming reactor 26. The reactor 26 is provided with the same type of catalyst used in the first or lead reactor 18.

In the heater 24 the mixture is heated to a temperature about the same as the temperature in the first heater 24. The heated mixture is at a pressure between about 100 and 500 p.s.i.g. The space velocity in reactor 26 is the same as in the first or lead reactor 18. In the second reactor, there is also a reduction in temperature due to the endothermic reaction but generally less than in the first reactor so that the efiiuent mixture from the second reactor is withdrawn from the bottom thereof through line 28 at a temperature between about 800 F. and 900 F. and passed through a third heater or furnace 32 before being passed through line 34 and introduced into the top of the last hydroformer reactor 36.

The temperature of the hydroformed products leaving heater 3-2 is between about 850 F. and 975 F., the pressure between about 100 and 500 p.s.i.g. and the space velocity between about 4 and 10 w./hr./w. The heated hydroformed products are then passed through line 34 into the top of the third hydroforming reactor 36 containing the same type of catalyst as the first and second hydroforming reactors 18 and 26. The temperature and pressure and other conditions in the last reactor 36 are substantially the same as in the first or second reactors 18 and 26.

According to the present invention, olefinic naphtha or naphthas are mixed with the efiluent from the third hydroformer 36 through line 38 for passage to hydrofiner 42 where the olefinic naphtha is partially hydrogenated. The olefinic naphtha may be a polymer gasoline or a catalytically cracked naphtha or a mixture of the two olefinic naphthas. Other olefinic gasolines such as visbreaker, thermal cracked or steam cracked naphthas may be used. The amount of olefinic naphtha introduced into line 38 may be between about 0.1 and 1.5 barrel per barrel of hydroformed naphtha passing through line 38 per hour.

Catalytically cracked naphtha boiling between about 75 F. and 400 F. can be passed through line 44 by pump 46 into line 38. Polymer gasoline boiling between about 75 F. and 425 F. can be passed through line 48 by pump 50 into line 38. The olefinic gasoline, which can be either catalytically cracked naphtha alone or polymer gasoline alone or a mixture of the two, is at a lower temperature than the hydroformed eflluent leaving reactor 36 and cools the efiluent to a temperature between about 400 F. and 700 F., depending on the amount of olefinic naphtha added and its temperature.

The mixture of hydroformed effluent and olefinic naphtha is passed through heater or cooler 52 to adjust the mixture temperature to between about 500 F. and 675 F. before passing it to the top of the hydrofiner 42. The mixture is passed down through the hydrofiner 42 at a temperature between about 500 F. and 675 F. and at a pressure between about and 500 p.s.i.g. The space velocity is between about 3 and 8 w./hr./w. and the hydrogen treat rate between about 1000 and 6000 s.c.f. of hydrogen per barrel of feed. The catalyst in hydrofiner 42 is preferably cobalt molybdate on alumina but other hydrofining catalyst, such as nickel tungsten on alumina, or nickel molybdate on alumina may be used. A silicaalumina support can be employed in place of alumina. In general, the sulfide form of the catalyst is used. Sulfiding is accomplished readily by well known techniques.

Hydrofining, particularly for saturating olefins, is a highly exothermic reaction. Since the hydroformed efiluent in line 38 has already been exposed to a hydrogen atmosphere in the presence of catalyst, it will not undergo any further reaction over cobalt molybdate catalyst. Therefore, the hydroformate acts as a heat sink or reservoir to control the exothermic hydrogenation reaction by absorbing some of the heat of reaction. The temperature rise in hydrofining reactor 42 is between about 25 F. and 100 F. and no cooling from an external source is needed. Hydrofining has no effect on hydroformate quality as the cobalt molybdate on alumina catalyst will not saturate monoaromatic hydrocarbons and no significant amount of cracking or isomerization will occur under these conditions.

Either catalytically cracked naphtha or polymer gasoline may be used but as the polymer gasoline is generally more olefinic than the catalytically cracked gasoline or naphtha, less of the polymer gasoline is used than the catalytically cracked gasoline when used either alone or in admixture.

When the polymer gasoline is used alone in admixture with the hydroformate liquid, the amount may be 5 to 40 vol. percent of polymer gasoline with the rest being the hydroformate liquid. When the catalytically cracked gasoline is used alone with the hydroformate liquid, the amount may be 5 to 60 vol. percent of the catalytically cracked gasoline with the rest being the hydroformate liquid. When a mixture of catalytically cracked naphtha and polymer gasoline is used and this mixture added to the hydroformate liquid, the mixture or blend of the catalytically cracked naphtha and polymer gasoline may range between about 5 and 60 vol. percent with the rest being the hydroformate liquid. Of the 5 to 60 vol. percent of the mixture or blend, the amount of polymer gasoline in this mixture or blend may range between about 20 and 60 vol. percent with the rest or 4080 vol. percent being the catalytically cracked gasoline.

The hydrofined mixture leaves the hydrofiner 42 through line 54 to gas-liquid separator 56 where gas is separated from the liquid. The gas passes overhead through line 58 and scrubber 62 to separate impurities from the hydrogen. The separated and clean hydrogenrich gas forms the recycle gas which is passed through line 12 for admixture with the naphtha feed in line 10. The hydrogen-rich gas contains about 65-90 mol percent hydrogen with the rest being light hydrocarbon gases.

The liquid is withdrawn from the separator 56 through line 64 and passed to stabilizer or fractionating tower 66 to remove C and C gases overhead through line 68. The liquid product which comprises high octane gasoline is withdrawn from the bottom of the stabilizer 66 through line 70.

polymer gasoline and the reformate liquids had the following analyses.

TABLE I.FEED STOCK ANALYSIS Reiormate Cat. Poly. Nap. Gas A B Gravity, API 55.4 70 46. 3 42. 9 Bromine Number 107. 6 114. 4 2. 5 2. 707 18 4 Nil 47 0. 1

192 86 124 126 238 224 226 253 286 342 301 295 F.B.P 316 412 358 364 RON plus 3 cc. TEL 96. 7 100.5 104.4 106. 7 MON plus 3 cc. TEL 83. 2 87. 8 94. 3 95.6 Sensitivity at 3 cc. TEL 13. 5 12. 7 10. 11. 1 Predicted Road Octane Index 1 93. 3 98. 2 104. 2 100. 5

1 Defined as A (RON) plus B (MON) plus 0 where A, B and O are arbitrarily selected constants.

In Example 1, Reformate A was mixed with the olefinic naphtha blend there described.

The hydrofining catalyst was cobalt molybdate on alumina containing 3.5 weight percent C00 and 12.5 weight percent of M00 on alumina, the naphtha feed rate was 5.1 w./hr./W. (4.8 v./v./hr.), average temperature was varied from 600 to 660 F. and the amount of H treat gas used was 3,000 s.c.f./b. of feed. The pressure was 300 p.s.i.g. Various degrees of bromine number saturation were obtained as is shown in the following Table H.

TABLE II.OCIANE CHANGES DUE TO HYDROFINING OLEFINIC NAPHTHAS OF EXAMPLE 1 Feed Hydrofined Products Hydrofining Temp, F 600 610 635 660 Bromine Number 60. 8 37. 7 33. 9 25. 7 20. 5 Percent Bromine Reduction 38 44 58 66 Sulfur, p.p.m 298 41 40 18 11 Motor Octane, plus 3 cc. TEL 87. 1 +1. 9 +1. 9 +1. 9 +2. 3 Research Octane, plus 3 cc.

TEL 100.2 0. 7 1.2 2.2 -2.7 Sensitivity, 3 cc. TEL 13. 1 2. 6 3. 1 4. 1 -5. 0 Predicted Road Octane Index. 97. 7 +0. 5 +0. 3 0. 6 0. 7

In certain cases, a refiner may be prepared to saturate olefins to a higher degree than to obtain motor octane. In such instances, the refiner will be giving away research octane. Both of the research and motor octanes are important.

EXAMPLE 2 In this example, a vol. percent blend of 35 vol. percent polymer gasoline and vol. percent of catalytic naphtha was mixed with 45% of hydroformate or Reformate B (see Table I). The same type cobalt molybdate on alumina catalyst was used, the same type polymer gasoline and catalytic naphtha as in Example 1 were used, the pressure was about 300 p.s.i.g., the feed rate was 4.9 v./v./hr. or 5.3 w./W./hr., the hydrogen gas feed rate was 3000 s.c.'f./b. of feed. The temperature was about 630 F.

TABLE III.OCTANE CHANGES DUE TO HYDROFINING OLEFINIC NAPHTHAS OF EXAMPLE 2 The data in Tables 11 and III show the octane number changes as a result of hydrofining of the two olefinic naphtha blends. Increased olefin saturation produced lower sensitivity products. At 44% olefin saturation or bromine number reduction (Table II), the Predicted RBad Octane index on the blend of Example 1 was improved by 0.3 and sensitivity reduced by 3.1. For the olefinic naphtha feed of Example 2 at about 52% olefin saturation the Predicted Road Octane index was increased by 0.4 unit and the sensitivity was reduced by 3.6 units.

Table IV includes data on hydrofining olefinic naphtha blends containing about 30% polymer gasoline and of Reformate liquid. The catalyst was the same type as used in Example 1, the naphtha feed rate was 3.4 v./ v./ hr. or 3.6 w./w./hr., the average temperature ranged from about 515 to 585 F., the pressure was 305 p.s.i.g. and the hydrogen treat gas used was 3,740 s.c.f./b. of feed.

TABLE IV.OCTANE CHANGES DUE TO HYDROFININGS3O% POLY GASOLINE AND 70% REFO RMATE FEED BLEND I-Iydro- Hydro- Hydro Product Feed 1 3 Product Feed 1 3 Product Hydrofining Temp., F 515 545 585 Bromine Number 32. 2 16. 0 33. 8 13.9 30. 7 7. 8 5O 50 1 Same poly gasoline as in Table I.

2 Reiormate B. 3 Reformate A.

From the above Table II data, it will be seen that depending on the degree of bromine number reduction, one can obtain various degrees of sensitivity reduction. A olefin saturation will thus give the maximum sensitivity reduction. Unfortunately at high olefin saturation levels, the loss in research octane is considerable, and is more than can be compensated by the increase in motor octane number. Thus it is desirable to only partially saturate the olefins so that there is very little loss in research octane yet there is a large gain in motor octane number. This optimum degree of olefin saturation depends on The data in Table IV also show that as bromine number reduction was raised from 50 to 75%, sensitivity lowering increased from 1.6 to 4.0 units. The sample with 59% ole-fin saturation gave the maximum road octane improvement coupled with substantial sensitivity reduction.

To con-firm that the reiormate was not afi ected in quality during the hydrofining step, the reformate was hydrofined by itself at similar conditions as the blend. These data are shown in Table V. Also octane results on the hydrofined blend of olefinic naphtha and reformate were compared to the values obtained on a blend of hythe type of olefinic naphtha but is usually close to 50%. 75 drofined naphtha and unhydrofined reformate. The

data in Table V show that the reform'ate octane number was not reduced by hydrofining.

The integrated hydrofiner of the present invention needs only one catalyst bed. The reformate liquid acts as a heat TABLE V.EFFECT OF HYDROFINING ON REFORMATE OCTANE QUALITY 1 Conditions were 040 F., 310 p.s.i.g., 2.3 v./v./hr. (2.6 w./w./hr.), 2,700 s.e.f./b. Hz.

2 Conditions were 630 F., 305 p.s.i.g., 4

3 Conditions were 574 F., 500 p.s.i.g., 3.5 v./v./hr. (3.6 w./w./hr.), 1,015 s.e.f./b. H2.

55% olefinie naphtha (65/35 Cat/Poly) and 45% Reiormate B.

EXAMPLE 3 In a specific example, a virgin naphtha having a boiling range of 180 F. to 355 F. is hydrofornied. About 2700 barrels/ day of this feed are desulfurized and then introduced into line 10, mixed with about 4000 s.c.f. of hydrogen per barrel of feed from line 1.2 and the mixture heated in furnace 16 to a temperature of about 975 F. The heated mixture is passed through hydroforming, reactors 18, 26 and 36 in series.

The inlet temperature of the feed mixture is about 975 F. and the temperature within the reactors 18, 26 and 36 is about 940 F. The pressure in the reactors 18, 26 and 36 is about 300 p.s.i.g. The catalyst in the reactors 1 8, 26 and 36 is 0.3 weight percent platinum on alumina containing halogen. The space velocity of the naphtha feed based on the total weight of platinum catalyst in all 3 reactors, 18, 26 and 36, is 1.5 w./hr./w.

About 2400 barrels of hydroformed naphtha blend per day pass through line 38 from the third hydroformer 36 to hydrofining reactor 42 which contains cobalt molybdate on alumina catalyst containing 3.5 weight percent of C and 12.5 weight percent M00 and the rest alumina. About 800 barrels per day of catalytic naphtha and 800 barrels per day of polymer gasoline are introduced into line 38 and mixed with the hydroformate therein. The resulting mixture is heated to a temperature of about 550 F. and passed through hydrofining reactor 42 to partially hydrogenate olefins in the olefinic naphtha to reduce the sensitivity of the olefinic naphthas. The temperature in the hydrofining reactor 42 is about 600 F. The pressure in reactor 42 is 300 p.s.i.g., the space velocity is about 5 v./v./hr. or 5.2 w./w./hr. at a high hydrogen treat rate of about 3,000 s.c.f./b. of feed.

The catalytic naphtha has a boiling range of about 192 F. to 316 F. and has a sensitivity of about 13.4. The polylmer gasoline has a boiling range of about 86 to 412 F. and has a sensitivity of about 13.0. The hydroformate in line 38 has a sensitivity of about 11.

Hydrofining releases heat in reactor 42 but as the reformate in line 38 has a sensitivity of about 11. hydroforming, the reformate has substantially no unsaturated hydrocarbons in it and hence, it serves as a heat reservoir or sink to control the exothermic hydrofining reaction. A rise of up to 100 F. in the hydrofining reactor can be tolerated.

Efiluent from reactor 42 is passed to separator 56 to separate gas from the total liquid product. About 12 million s.c.f. per day of hydrogen-containing gas pass overhead through line 58. About 4000 barrels/day of hydroformate and partially saturated olefinic naphthas are recovered and passed through line 64- to fractionator 66 from which about 2300 barrels/day of C to 400 F. hydroformate are recovered. The sensitivity of the hydroformate including the partially hydrogenated polymer gasoline and catalytic gasoline is 9.4.

With the present invention, the normal Powerformer separator and stabilizer can be used and this results in considerable cost saving.

sink or reservoir to absorb or remove exothermic heat of hydrofining. A separate hydrofiner for treating the catalytic gasoline or polymer gasoline would require multicatalyst beds with cold hydrogen quench between each catalyst bed for temperature control, or some other form of cooling would be necessary. High hydrogen treat gas rates are readily obtained in the present invention and result in more efficient hydrogenation for a given pressure and temperature than can normally be obtained.

With the present invention either catalytic naphtha alone or a polymer gasoline alone can be mixed with the reformate in line 38 for passage to the hydrofiner 42 or a mixture or blend of the catalytic naphtha and polymer gasoline may be used. The polymer gasoline is easier to hydrofine and gives a higher octane number improvement.

In time, the cobalt molybdate catalyst will need to be regenerated, although the frequency will generally be considerably less than the platinum hydroforming catalyst. Regeneration is acocmplished by burning the carbonaceous deposits from the catalyst using a diluted air stream. After regeneration, the catalyst may be given an activation step by reacting the catalyst with a suitable sulfiding agent such as sulfur containing oil, hydrogen sulfide, carbon disulfide and the like.

What is claimed is:

1. A method of improving sensitivity of olefinic naphtha which comprises hydroforming a naphtha feed in admixture with a hydrogen-containing gas under hydroforming conditions in a series of hydroforming reactors, the inlet temperature in each hydroforming reactor being in the range of about 850 to about 975 F., and then mixing an olefinic naphtha with the hydroformed material leaving the last hydroforming reactor and passing the said mixture through a hydrofining reactor under hydrofining conditions to partially saturate said olefinic naphtha and product a naphtha product of lower sensitivity.

2. A method according to claim 1 wherein said olefinie naphtha comprises a feed selected from the group of catalytically cracked naphtha, thermally cracked naphtha, steam cracked naphtha, polymer gasoline and mixtures thereof.

3. A method according to claim 1 wherein about 5 to 40 vol. percent of polymer gasoline and 60 to vol. percent of hydroformed material are used.

4. A method according to claim 1 wherein about 5 to 60 vol. percent of catalytically cracked gasoline and 40 to 95 vol. percent of hydroformed material are used.

5. A method according to claim 2 wherein 5 to 60 vol. percent of a blend of catalytically cracked gasoline and polymer gasoline and the rest hydroformed material is used and said blend comprises 40 to 80 vol. percent of catalytically cracked gasoline and the rest polymer gasoline.

6. A method which comprises passing a naphtha feed and hydrogen-containing gas over a platinum on alumina catalyst containing halogen in a series of hydroforming reactors maintained at an inlet temperature between about 850 F and 975 F., a pressure between about to 500 p.s.i.g., a feed rate between 1 and 3 w./w./hr. and with between about 3000 and 7000 s.c.f. of hydrogen per barrel of feed, mixing an olefinic naphtha with the effluent from the last hydroforming reactor in an amount between about 5 and 60 vol. percent of said naphtha based on the total volume of the resulting mixture, passing said mixture over a hydrofining catalyst in a hydrofining reactor maintained at a temperature between about 500 F. and 675 F., a pressure between about 100 and 500 p.s.i.g., a space velocity between about 3 and 8 w./w./hr. and an amount of hydrogen-containing gas between about 1000 and 6000 s.c.f./b. of feed, recovering a hydrofined efiluent, separating gas from liquid in said hydrofined liquid and fractionating said separated liquid to recover a gasoline of improved sensitivity.

7. A method which comprises passing a naphtha feed and hydrogen-containing gas over a platinum on alumina catalyst in a series of hydroforming reactors maintained at hydroforrning temperature and pressure, mixing an olefinic naphtha with the efliuent from the last hydroforming reactor in an amount between about 5 and 60 vol. percent of said naphtha charge based on the total volume of the resulting mixture, passing said mixture over a hydrofining catalyst in a hydrofining zone maintained under hydrofining conditions of temperature and pressure and in the presence of hydrogen, recovering a hydrofined eflluent, separating gas from liquid in said hydrofined efliuent and recovering a gasoline of improved sensitivity from said liquid.

8. A method according to claim 7 wherein said olefinic naphtha comprises a feed selected from the group of catalytically cracked naphtha, polymer gasoline or a mixture of a catalytically cracked naphtha and a polymer gasoline.

References Cited UNITED STATES PATENTS 2,423,328 7/1947 Layng 20864 2,684,325 7/ 1954 Deanesly 20864 2,877,172 3/1959 Morbeck et a1. 20897 3,070,637 12/1962 Honneycutt 20865 HERBERT LEVINE, Primary Examiner.

US. Cl. X.R. 20865, 97, 144 

